Interpretive Summary: Two trials were conducted to evaluate the ability of condensed tannin to protect the omega-3 fatty acid called alpha-linolenic acid (ALA) from hydrogenation by microbes in the rumen of beef cattle. In the first trial, five steers were given a grain-based diet during the whole trial but given the ground flaxseed either treated with condensed tannin or not treated during the two periods of the trial while another five steers were given a forage-based diet for the whole trial but given the ground flaxseed either treated or not treated during the two periods. Ingestion of tannin-treated flaxseed raised ALA and total omega-3s (ALA and EPA) in neutral lipids of blood plasma 6.8 and 7.4%, respectively, only when steers ate forage. A second trial using in vitro fermentation was conducted to determine if addition of casein to the flaxseed before treating it with tannin was warranted. Samples were incubated with bovine rumen fluid for 0, 12, and 24 hours. Adding casein to flaxseed before treating it with condensed tannin did not reduce hydrogenation of ALA when compared to tannin alone, which reduced hydrogenation of ALA to 13% over 24 hours compared to 43% for untreated flaxseed. Thus, we demonstrated that treating ground flaxseed with condensed tannin can be used to increase the level of ALA in the neutral lipid of bovine blood plasma, which may lead to increased enrichment of bovine muscle tissue with ALA as well as other omega-3 fatty acids.

Technical Abstract:
Two trials were conducted to evaluate the ability of condensed tannin to protect 18:3n-3 from hydrogenation by microbes in the rumen of beef cattle. In the first trial, ten steers were used in a trial with a split-plot design with flaxseed treatment (none or tannin-treated) as the main plot and the basal diet (grain or forage) as the sub-plot. Five steers were given a grain-based diet during the whole trial but given the ground flaxseed either treated with condensed tannin or not treated during the two periods of the trial while the other five steers were given a forage-based diet for the whole trial but given the ground flaxseed either treated or not treated during the two periods. Ingestion of tannin-treated flaxseed raised 18:3n-3 and total n-3s (18:3n-3 and 20:5n-3) in neutral lipids of blood plasma 6.8 and 7.4%, respectively, only when steers ate forage. A second trial using in vitro fermentation was conducted to determine if addition of casein to the flaxseed before treating it with tannin was warranted. Samples were incubated with bovine rumen fluid for 0, 12, and 24 hours. Adding casein to flaxseed before treating it with condensed tannin did not reduce hydrogenation of 18:3n-3 when compared to tannin alone, which reduced hydrogenation of 18:3n-3 to 13% over 24 hours compared to 43% for untreated flaxseed. Thus, we demonstrated that treating ground flaxseed with condensed tannin can be used to increase the level of 18:3n-3 in the neutral lipid of bovine blood plasma, which may lead to increased enrichment of bovine muscle tissue with 18:3n-3 as well as other n-3 FA.